The retinal pigment epithelium (RPE) forms a major portion of the blood retinal barrier and helps to maintain the environment required for normal retinal activity. Although disruption of the RPE blood-retinal barrier and RPE transport have been associated with clinical disease, very little is known about the precise nature of these functions. The long term goal of this research is to fully characterize the transepithelial transport and barrier properties of human RPE so that clinical disease in humans can be more completely understood, more effectively treated and, possibly, even prevented. We have developed a preparation of cultured fetal human RPE that is well suited for studies of RPE transport. Using this preparation, we have collected preliminary data which suggests that the results of the experiments we propose to do during the next grant period may lead to a better understanding and possible treatment or prevention of specific human diseases. During the next grant period, we propose: 1)to characterize cultured fetal human RPE transepithelial transport by extending Ussing chamber studies using pharmacologic probes, ion manipulation, and isotope flux studies. 2)to determine how cultured fetal human RPE transepithelial transport is modulated by intracellular cyclic AMP. 3)to determine the degree to which cultured fetal human RPE transepithelial transport may be regulated by extracellular receptors (such as those to beta adrenergic agents) and to determine the degree to which cultured fetal human RPE transepithelial transport is affected by agents (such as (IBMX) that alter intracellular cyclic AMP metabolism. 4)to incorporate measurements of trans-RPE fluid fluxes into these studies so that fluid fluxes can be measured directly rather than calculated from isotope fluxes which are subject to cumulative experimental errors.